1. Field of the Invention
The present invention relate generally to the patterning of refractory metals, and in particular to the reduction of undercutting during the etching of refractory metal patterns.
2. Description of the Background Art
Refractory-metal plasma-etching is commonly used to pattern interconnects for integrated circuits. In particular, reactive-ion-etching (RIE) is used to pattern refractory metals, such as tungsten and tantalum, on masks or x-ray lithography. To meet the demand for critical dimension (CD) control in x-ray lithography, the absorber must be patterned with the minimum possible undercut, i.e., with vertical or essentially vertical sidewalls. As linewidths decrease, this requirement becomes much more stringent. Previous works have shown improvement in linewidth control through the use of polymeric sidewall passivation. In one process, a fluorocarbon gas was introduced in the chamber along with the etch gas. Polymer by-products were believed to be deposited on the sidewalls of the etched metal, thereby passivating it. The mechanisms for this deposition were not well-understood, and it was not known how the fluorocarbon gas affected the etch rate of the metal.